Method for the separation of rare earths



Unite States Patent METHOD FOR THE SEPARATION OF RARE EARTHS MarxHirsch, New York, and Raymond F. Bacon, Bronxville, N. Y., and Emil A.Lucas, Washington, Pa., assignors to Molybdenum Corporation of America,New York, N. Y., a corporation of Delaware No Drawing.ApplicationOctober 30, 1952, Serial No. 317,842

5 Claims. (Cl. 23-19) The invention relates to a method for theseparation of rare earths. More particularly, it pertains to a procedurefor the separation of rare earths from an ore, e. g. a rare earths oreoccurring at Mountain Pass, California, and includes correlatedimprovements and discoveries whereby the obtention of a product having arelatively high content of rare earth compounds is facilitated. The rareearths referred to herein, it will be understood, are those elementshaving an atomic number 57-71, inclusive, and of especial interest, arecerium, lanthanum, praseodymium, neodymium, terbium and Samarium.

An object of the invention is the provision of a method in accordancewith which rare earths, present largely as oxides, carbonates, andfluorocarbonates in varying proportions, are selectively separated froman ore containing them and from concentrates of such ores.

A further object of the invention is to provide a method whereby rareearth compounds are obtained from an ore by treatments with acid atdiffering concentrations.

Another object of the invention is the provision of a procedure inaccordance with which rare earths may be obtained readily, efiicientlyand economically from natural sources.

An additional and more particular object of the invention is to providea method whereby rare earth compounds are separated from a lime-the termlime as used herein will be understood to refer to calcium carbonatealone and in conjunction with one or more of the group calcium oxide,and barium, strontium and magnesium compounds usually as carbonates andoxides-containing ore by selective solvent action-with an inorganic aciOther objects of the invention will in part be obvious and will in partappear hereinafter.

-The invention accordingly comprises the several steps and the relationof one or more of such steps with respect to each of the others thereof,which will be exemplified in the method hereinafter disclosed, and thescope of the invention will be indicated in the claims.

In the practice of the invention, rare earths, usually occurring in theform of oxides and carbonates, and in some instances asfiuorocarbonates, may be separated from an ore containing them bytreating the ore in comminuted condition with a dilute inorganic acid,specifically, and by way of illustration, hydrochloric acid, separatingliquid and' solid, and then subjecting separated solid to treatment withmore concentrated hydrochloric acid.

Further, the dilute hydrochloric acid suitably is of a concentrationfrom about 0.5 to about 5.0%, particularly,

about 1%, and the more concentrated hydrochloric acid desirably has aconcentration from about 17% to about 35%, and preferably about 30%. Itmay be mentioned that the acid concentration and the amount thereof fromthe theoretical, may vary both as to the first stage and as to thesecond stage, according to the temperature and time conditions.

Moreover, the treatment may extend over a period of time which may befrom about one hour to about five ice hours specifically, about threehours. The procedure leads to the preparation of a product which has arelatively high content of rare earth compounds and such content,usually constitutes the major proportion of the product obtained.

The treatment with differing concentrations of acid, is especially welladapted for the treatment of the rare earths containing ore that occursat Mountain Pass, California. This has been classified by the U. S.Geological Survey as a Bastnasite type of ore and contains rare earthslargely as oxides and carbonates or fiuorocarbonates. Such an oreordinarily contains barium sulphate, silica and lime in a majorproportion.

More particularly, the rare earths may be separated from a Bastnasitetype of ore having the following approximate percentage composition:barium sulphate 20-40; silica 15-25; lime 2-30; rare earth compounds5-40; iron oxide l-5; and aluminum oxide l-5. If desired and preferably,the naturally occurring ore may be concentrated, as by flotation, orgravity, or other, prior to being subjected to treatment with acid.

When an ore having the approximate composition just above mentioned hasbeen concentrated, i. e. a mill concentration, such concentrate willusually have the following approximate percentage composition; bariumsulphate 10-30; silica 2-10; lime 5-15, and rare earth compounds 40-60.

The treatment of the concentrate is conducted in the same manner,namely, first with a dilute hydrochloric acid which may have aconcentration from about 0.5 to about 5.0% and subsequently with moreconcentrated hydrochloric acid containing from about 17% to about 35%.Furthermore, it may be added that milling by-products commonly referredto as middlings and as tails can be treated in the manner describedherein.

As an illustrative embodiment of a manner in which the invention may bepracticed, the following examples are presented:

EXAMPLE I Leaching to remove lime A Bastnasite type run-of-the-mine orecontaining about 20% rare earth oxides, about 15% lime, about 3% ironand aluminum oxides, and the remainder consisting of primarily, bariumsulphate and silica, and about thereof being of mesh, was introducedinto about 12,000 mi. of water in an amount of about 4,500 gms.following which, about 2,350 ml. of hydrochloric acid of suitableconcentration to give a concentration thereof in the mixture of about1%, were added over a period of about 40 minutes.

After the acid had been added, the mixture was agitated for a period ofabout two hours. The mixture was then permitted to settle and the cloudysupernatant liquid containing some'barium sulphate and silica wasdecanted and discarded. The residue was washed twice by slurrying withabout 4,500 ml. of water for 20 minutes and allowed to settle each timefor about two hours with the supernatant liquid being decanted anddiscarded in each case. The residue thus obtained was dried at C.

Extraction of rare earths being decanted and subsequently utilized forthe separation of iron.

The residue was slurried with water for about 30 minutes, the mixtureallowed to settle and the supernatant liquid decanted and being setaside for re-use in a subsequent operation.

Separation of iron About ml. of 3% hydrogen peroxide was added for each100 ml. of the extract containing the rare earths. The solution wasboiled until the hydrogen peroxide was expelled whereupon it was allowedto cool and solid sodium carbonate added with agitation until a pH valueof about 1.0 is reached. Then, a saturated solution of sodium carbonate,i. e. approximately 32%, was added with agitation until a pH value ofabout 3.6 was obtained. During the addition of the sodium carbonate, ared precipitate is formed which settles out upon standing. Thesupernatant liquid was decanted, a filter aid added thereto and themixture filtered with the obtention of a filtrate having a clear tancolor.

The red residue was placed in a cloth type of filter press and thefiltrate obtained therefrom was combined with that previously obtainedafter being slurried with a filter aid which was subsequently removed byfiltration. The red residue or precipitate was dried at 110 C. thenslurried with water at a pH value of about 3.6 for about half an hourwhen it was allowed to settle and the supernatant liquid decanted andutilized in subsequent operations.

Separation of rare earth carbonates The tan filtrate was placed in asuitable receptacle and a 32% solution of sodium carbonate slowly addedthereto with agitation and until a pH value of about 6.1 was reached.The mixture was then digested with agitation at about the boiling pointfor a period of about one hour. It was then allowed to cool and settleovernight with the supernatant liquid being decanted and the whiteresidue or precipitate slurried with a maximum amount of water dependingupon the size of the reaction vessel, the water having been adjusted toa pH value of about 5.0. During the slurrying, the pH value of themixture was adjusted to about 6.1 and the mixture allowed to settle. Thewashing or slurrying was repeated until substantially all of the calciumhad been eliminated.

Conversion to rare earth chlorides The rare earth carbonates obtained asjust above described and containing an amount of water just suflicientfor easy handling were added at a convenient rate to about 200 ml. ofboiling B. hydrochloric acid until the carbonate was no longer solubleand a brown mixture formed at a pH value of about 4.2. The hot tanmixture was filtered and the residue slurried with a convenient amountof water for handling purposes. This mixture was then added at aconvenient rate to about 300 ml. of boiling 20 B. hydrochloric acid withthe mixture being definitely on the acid side and of a muddy yellowcolor. More of the rare earth carbonates was then added until the yellowturned to brown with the mixture being filtered and the procedurerepeated until all of the rare earth carbonates have been utilized andonly a small amount of undissolved brown residue remains.

All of the filtrates were combined and boiled at a convenient rate toavoid excessive foaming until the temperature of the solution reached138 C; The solution containing the rare earth chlorides was then pouredinto moulds and allowed to cool. The amount of acid and rare earthcarbonates to be used must be estimated in view of the fact that thematerial to be dissolved in the acid contains undetermined proportionsof the differently soluble rare earths and water, consequently, moreacid or more rare earth carbonates will he added at the various steps inthe procedure in the event that there is an insufiicient volume at thatstep.

4 EXAMPLE n A concentrate of Bastnasite type of ore from Mountain Pass,California and containing about rare earths expressed as oxides andabout 10% of lime expressed as calcium oxide, the remainder beingsubstantially barium sulphate and silica, was leached with dilutehydrochloric acid to remove lime and the rare earths extracted from theproduct so obtained and subsequently separated as carbonates andchlorides in the manner described in Example l.

The procedure hereinabove described alfords a ready and economic mannerin which rare earths may be sep arated from a Bastnasite type of ore inwhich they occur. Moreover, the inorganic acid utilized may be nitricacid or sulfuric acid instead of hydrochloric acid, depending on thecharacter of the ore, and also somewhat on the prevailing economicconditions. Further, these acids may be employed in suitable compatibleadmixture and in combination, thus the dilute stage, or step, could bewith hydrochloric acid and the more concentrated stage with nitric acid.As above indicated, the product obtained will consist predominantly ofrare earth compounds, e. g. chlorides, that is those compounds will bepresent in an amount greater than Further, the product contains the rareearth compounds in a relatively high con centration, i. e. markedlyhigher than by procedures heretofore used.

Additionally, the differing concentrations of the acid must be carefullycontrolled within the ranges given inasmuch as should the initialtreatment, or stage, be carried out with acid of lower concentration, aconsiderable amount of the lime would remain in the product subsequentlytreated with the stronger acid, and if the concentration is greater thanthat mentioned, there would be a loss of rare earth compounds due tosolution thereof and consequent passing into the liquid. Furthermore,the more concentrated acid must be within the concentration range givendue to the fact that a lower concentration would fail to separate someof the rare earth compounds and a higher concentration would not only beuneconomical but would lead to the solution also of undesirableconstituents.

A marked advantage of the procedure is that it leads to the productionof rare earth compounds in a physical form and in a condition of puritywhich renders them markedly well adapted for the obtention therefrom ofa variety of other compounds such as chloride, oxide, hydrate, oxalate,etc. which may be used in industry for the production of rare earthcontaining metals or compounds that are employed in the production ofsparking alloys, ferrous and non-ferrous metallurgic products, ceramicsand others. In addition, the procedure is characterized by the followingadvantageous features: (a) economic operation; (b) satisfactory yieldsof the rare earths; (c) the product obtained being suitable for andwhich may be readily converted into other materials for various uses;and (d) the apparatus or extraction units required are neither elaboratenor costly and from which a relatively high tonnage may be obtained.

Since certain changes may be made in carrying out the above methodwithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be illustrative andnot in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire tosecure by Letter Patent is:

1. A method for the separation of rare earths from a Bastnasite type orewhich comprises treating such an ore in comminuted condition with adilute inorganic acid selected from the group consisting ofhydrochloric, sulfuric and nitric acids having a concentration fromabout 0.5 to about 5.0% whereby lime is removed by solution thereof,separating solid and liquid, said solid containing rare earths and saidliquid containing lime in solution, then subjecting separated rareearths containing solid to treatment with a more concentrated inorganicacid selected from the group consisting of hydrochloric, sulfuric andnitric acids having a concentration from about 17% to about 35% andseparating solution containing rare earth salts of said acid fromundissolved material whereby a solution containing rare earth salts isobtained, said solution being adapted for recovery of rare earthcompounds therefrom.

2. A method for the separation of rare earths from a Bastnasite type orewhich comprises treating such an ore in comminuted condition with dilutehydrochloric acid having a concentration from about 0.5 to about 5.0%,whereby lime is removed by solution thereof, separating solid andliquid, said solid containing rare earths and said liquid containinglime in solution, then subjecting separated rare earths containing solidto treatment with hydrochloric acid having a concentration from about17% to about 35%, and separating solution containing rare earth salts ofsaid acid from undissolved material whereby a solution containing rareearth salts is obtained, said solution being adapted for recovery ofrare earth compounds therefrom.

3. A method for the separation of rare earths from a Bastnasite type orewhich comprises treating such an ore in comminuted condition withhydrochloric acid having a concentration of about 1%, whereby lime isremoved by solution thereof, separating solid and liquid, said solidcontaining rare earths and said liquid containing lime in solution, thensubjecting separated rare earths containing solid to treatment withhydrochloric acid having a concentration of about 30% at a temperatureof about 80 C., and separating solution containing rare earth salts ofsaid acid from undissolved material whereby a solution containing rareearth salts is obtained, said solution being adapted for recovery ofrare earth compounds therefrom.

4. A method for the separation of rare earths from a Bastnasite type orewhich comprises treating a concentrate of such an ore in comminutedcondition with dilute hydrochloric acid having a concentration fromabout 0.5 to about 5.0%, whereby lime is removed by solution thereof,separating solid and liquid, said solid containing rare earths and saidliquid containing lime in solution, then subjecting separated rareearths containing solid to treatment with hydrochloric acid having aconcentraion from about 17% to about and separating solution containingrare earth salts of said acid from undissolved material whereby asolution containing rare earth salts is obtained, said solution beingadapted for recovery of rare earth compounds therefrom.

5. A method for the separation of rare earths from a Bastnasite type orewhich comprises treating such an ore containing barium sulphate, silicaand lime in a major proportion with hydrochloric acid having aconcentration from about 0.5 to about 5.0%, whereby lime is removed bysolution thereof, separating solid and liquid, said solid containingrare earths and said liquid containing lime in solution, then subjectingseparated rare earths containing solid to treatment with hydrochloricacid having a concentration from about 17% to about 35% at a temperaturefrom about to about C., and separating solution containing rare earthsalts of said acid from undissolved.

material whereby a solution containing rare earth salts is obtained,said solution being adapted for recovery of rare earth compoundstherefrom.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR THE SEPARATION OF RARE EARTHS FROM A BASTNASITE TYPE OREWHICH COMPRISES TREATING SUCH AN ORE IN COMMINUTED CONDITION WITH ADILUTE INORGANIC ACID SELECTED FROM THE GROUP CONSISTING OFHYDROCHLORIC, SULFURIC AND NITRIC ACIDS HAVING A CONCENTRATION FROMABOUT 0.5 TO ABOUT 5.0% WHEREBY LIME IS REMOVED BY SOLUTION THEREOF,SEPARATING SOLID AND LIQUID, SAID SOLID CONTAINING RARE EARTHS AND SAIDLIQUID CONTAINING LIME IN SOLUTION, THEN SUBJECTING SEPARATED RAREEARTHS CONTAINING SOLID TO TREATMENT WITH A MORE CONCENTRATED INORGANICACID SELECTED FROM THE GROUP CONSISTING OF HYDROCHLORIC, SULFURIC ANDNITRIC ACIDS HAVING A CONCENTRATION FROM ABOUT 17% TO ABOUT 35% ANDSEPARATING SOLUTION CONTAINING RARE EARTH SALTS OF SAID ACID FROMUNDISSOLVED MATERIAL WHEREBY A SOLUTION CONTAINING RARE EARTH SALTS ISOBTAINED, SAID SOLUTION BEING ADAPTED FOR RECOVERY OF RARE EARTHCOMPOUNDS THEREFROM.